1. Field of the Invention
This invention relates generally to the field of biomass cultivation and more particularly to a system and method for cultivation of ocean vegetation on a movable support system with automated position and depth control.
2. Description of the Related Art
The world is relatively rapidly running out of oil. In the U.S., the discovery of new oil resources, and the rate of production, peaked many years ago. Roughly in parallel with the situation in the U.S., the peak of world production has lagged the peak in discovery by a few decades, and is expected to occur in the near future. This will be followed by a long period of decline as oil wells produce less and less even as they are given more and more elaborate “encouragement”. Some say that production will peak in this decade; other say it will be a few more years before the peak is reached. Alternative sources of energy that can adequately replace the shortfall of oil in both price and production volume are not apparent. This problem is huge—currently the world consumes energy at the rate of about 1.3×1013 Watts, which is ˜2 kW continuously for every person on Earth. In the U.S., per capita consumption is closer to 10 kW. At $100 per barrel of oil, the raw cost of energy is about 6 cents per kilowatt-hour (in the form of heat, not electricity). At $3.50 per gallon of gasoline, the cost is almost 10 cents per thermal kWh. The largest fraction of the energy used by civilization comes from oil, at a dollar value of several trillion dollars per year. Oil production is presumed to decline over the next century roughly as a mirror-image of the way it has grown over the past century. Even without addressing the huge problem of greenhouse gasses, the nation and the world need to provide an alternative energy source to replace the oil resource that is fast being consumed.
Solar energy falls on the Earth in an abundant, if diffuse, way. The power of sunlight arriving continuously at the Earth's surface is about 1017 Watts—almost 10,000 times the rate that power is used by all of humanity. Perhaps most importantly, this power can be collected and used in a way that does not upset either the thermal balance of the Earth (since it falls here naturally anyway) or the balance of gasses in the atmosphere (since using it does not intrinsically involve the net release of gasses that change the absorption or emission properties of the atmosphere).
The key problem of solar energy is that it is so diffuse: it provides only about 1000 W/m2 at peak brightness and ˜160 W/m2 at any typical point on the Earth's surface averaged over the entire year. At 6 cents per kWh (the thermal equivalent to oil at $100/barrel), this means that each square meter of solar collector only generates about $86 in energy value per year, even if converted at 100% efficiency. The conversion efficiency for solar power to electricity currently ranges downward from about 30%, so that each square meter of solar collector generates perhaps $25 in gross economic return per square meter per year (although electricity generally sells for several times the price of thermal energy). This price of energy is too low for any “high tech” solution to be viable, since a traditional economic rule-of-thumb is that the capital investment can be no greater than three years gross sales, and hopefully less. Currently photovoltaic solar arrays, for example, have a capital cost that is many times the value of the power that they can generate in a year. For example, at a typical photovoltaic array cost of $3 per peak Watt and operating for 1400 peak-equivalent hours per year, the time to return the capital cost of the array if the electricity were sold at 10 cents per kWh is 22 years. Any basic energy source, which is offered to replace oil and not cause an upheaval in the world economy, must have a price close to or below 6 cents per kWh of thermal energy, or 10-15 cents per kWh of electrical energy.
In the early 1970s a solution to this overall problem was suggested by Dr. Howard A. Wilcox of the U.S. Naval Ocean Systems Center. (Dr. Wilcox, deceased in 1994, was the father of the inventor in the present application.) This solution was to use ocean farming to provide relatively inexpensive energy (and food) for the world's populations. Working with Professor Wheeler North of Caltech and with funding from the U.S. Navy, the National Science Foundation, the American Gas Association, and others, he deployed a small test farm that showed that fast-growing marine plants (especially Macrocystis Pyrifera, the “California Giant Kelp”) can convert over 1% of the incident sunlight into useful stored chemical energy. He envisioned using nutrients from the deep ocean. Most of the ocean is a photosynthetic “desert” because the surface waters are so nutrient-poor—in places where upwelling from deeper layers is natural, such as the Sargasso Sea, there is abundant photosynthetic activity. Dr. Wilcox proposed large farms—typically 100,000 acres—that each would consist of a huge “net” with a grid spacing of several meters to which all the plants would be affixed. Dr. Wilcox demonstrated that the cost of this substrate would be much too expensive if the farm were anchored to the bottom and had to withstand the forces of currents, waves, and storms. Instead, he envisioned farms that floated freely and used a propulsion system to give fine control to keep them circulating around in the large eddy patterns in the oceans.
While Dr. Wilcox showed that such farms could be economical if made large enough, he cautioned (see “Hothouse Earth”, Wilcox, Howard A., Praeger 1975) that the fundamental problem remained that Organization of Petroleum Exporting Countries (OPEC) oil producers could and did systematically drive any new alternative energy sources out of the market through their total control of the price of energy. Since the production cost of a barrel of oil for some countries at that time was approximately $0.25, and it was selling for $20 or more, the OPEC countries (especially Saudi Arabia) could manipulate the price of energy so that any investment in alternative sources of energy could be systematically undermined or obliterated. Dr. Wilcox noted that any fledgling alternative energy sources must be protected by government edict if they were to thrive. The particular advantages of ocean farming are that the surface area in the ocean is “free”, that the necessary nutrients required to nurture the plants lie only a few hundred meters below the sunlit surface waters, that the biomass generated makes an almost ideal feedstock into both of the existing food and energy distribution networks, and that the growth of these plants results in no net production of greenhouse gasses or thermal pollution. The use of this biomass as food is attractive because dried kelp can be fed directly to farm animals, replacing feedstocks that currently sell for much more than oil. Kelp can be composted directly into natural gas at extremely high efficiency in only a few weeks, and the resulting natural gas can be injected into the distribution grid or can be readily converted into gasoline, jet fuel, or other common petrochemical commodities.
A major problem with the huge kelp farms envisioned by Dr. Wilcox is the very large capital cost of the system. In order to produce a net return, the farms envisioned by Dr. Wilcox would have to be extremely large. This is due to the more-or-less fixed minimum size of any large upwelling apparatus that brings up nutrient-rich water from depth (typically 300 m deep), and the scaling laws that govern the design of the large “propulsors” (diesel or wave-powered propellers) that keep the farm from running aground. Dr. Wilcox conjectured that the overall efficiency of the farm might be increased from the 1% that he and Dr. North had demonstrated to about 2%, at which point the large farms he envisioned would be economical. Another major problem with these farms is that the upwelling of large amounts of cold, deep water will change the surface temperature of the oceans and change the rates that water vapor or other gasses exchange between the surface waters and the atmosphere. The effect of these changes on the global climate are unknown, but are possibly large given the tremendous area of the farms needed if there is to be a significant effect on the global production of food and energy.
It is therefore desirable to provide a system for ocean biomass production that is economical even at relatively small scale and at the demonstrated 1% efficient conversion of sunlight to stored chemical energy, and without requiring upwelling of significant amounts of deep water to the ocean surface in ways that might have unforeseen impacts on the Earth's climate.